The present invention generally relates to a leadscrew assembly and, in particular, relates to one such leadscrew assembly having a roller nut interface with a leadscrew.
Leadscrew arrangements are known in the art and are used to convert rotary motion of a shaft of a screw into linear motion of a fixture interfacing with the screw.
Typically, for discussion purposes, conventional precision leadscrew arrangements are separable into two categories, i.e. those arrangements having a static nut and those arrangements having a recirculating ball nut. Typically, a static nut/leadscrew arrangement employs a solid internally threaded nut and a solid leadscrew. A recirculating ball nut/leadscrew arrangement typically utilizes a nut of recirculating steel balls and a specially threaded steel shaft.
Both of these arrangements have drawbacks that must be accepted and dealt with in deciding which arrangement to use for a given application. The static nut/leadscrew arrangement is relatively inexpensive but exhibits rather high friction and excessive wear. As such, the static nut/leadscrew arrangement requires frequent lubrication and monitoring. As a result certain constraints are placed upon any system employing such an arrangement to ensure proper and appropriate lubrication.
The recirculating ball nut/leadscrew arrangement, while requiting a minimum lubrication does, however, require a ball recirculating mechanism that is space consuming. Typically, such an arrangement is relatively expensive, although it is a more precise mechanism than comparable static nut/leadscrew arrangements. Nevertheless, such a mechanism limits the pitch of the leadscrew to be coarse or have a high pitch, that necessitates the use of a torque increasing gearbox between the drive motor and the leadscrew, introducing backlash and other attendant difficulties into the rotary to linear motion conversion.
It is clear from the above discussion that a leadscrew arrangement that overcomes the above recited difficulties of high friction, frequent lubrication, and which eliminates the requirement for a torque increasing device and which is relatively inexpensive is very much needed and desirable in the precision leadscrew field.